Automatic release welding circuits



Feb. 14, 1939. 1 g E- 2,147,468

AUTOMATIC RELEASE WELDING CIRCUITS Filed Oct. 9, 1937 WITNESSES: INVENTOR 07 WM Fia/p/v N Szoddarafi ATTONE Patented Feb. 14, 1939.

UNITED STATES PATENT OFFICE AUTOMATIC RELEASE WELDING CIRCUITS Pennsylvania Application October 9,

1 Claim.

My invention relates to welding circuits, and especially to welding circuits in which a discharge device is inserted to pass the welding current therethrough.

An object of the invention is to automatically release the application of the welding electrodes from the parts being welded upon completion of a predetermined number of half cycles of welding current.

Another object of my invention is to provide automatic means for controlling both the application of the welding current and the welding electrodes to the work.

At the present time, welders apply the elect trodes to the work and when they judge the work has been completed, the electrodes are withdrawn and applied to the next work to be welded. In assembly lines of present day mass producing manufacturing establishments, it is apparent that the exact number of half cycles of welding current can be predetermined that will do the welding job exactly because one job will be exactly like the next waiting in line. In such an assembly line the expenditure of extra half cycles of welding current and the extra time taken by the workmen in performing the welding operation over that necessary to complete the weld will be multiplied by the large number of units which the workmen will weld in a day and will amount to a .large amount of unnecessary expenditure of electricity and time. It is, accordingly, an'object of my invention to provide automatic means by which the welding current will be applied for the necessary number of half cycles of welding current, and at the conclusion of these necessary half cycles of welding to the work, at least one of the electrodes will be automatically withdrawn from the work, so that the apparatus can be applied to the next job in the assembling line.

Other objects and advantages will be apparent from the following description and drawing, in which the single figure is a diagrammatic view illustrating a preferred embodiment .of my invention.

Referring to the figure of the drawing, the reference character Ill designates generally a Welding transformer having a primary winding 50 and a secondary winding |2. The secondary winding I2 is connected to the customary welding circuit in which the welding electrodes l3, M are diagrammatically represented applied to objects l5 which are to be welded together. The primary winding H of the transformer is connected 1931; Serial No. 168,208

by means of conductors l6 and I! to a source of alternating current.

In order to control the application of the welding current from the source of alternating current to the transformer I0, vapor electric devices shown generally at l8 and I9 are provided. The devices l8 and I9 are of the mercury vapor type having an anode and a mercury pool 2| as a cathode in the bottom of a container 22. In order to render the vapor electric devices Hi and |9 conducting, a startingelectrode 23 is provided.

Although other types of starting electrodes may be utilized, I prefer to use a high resistance electrode immersed in the mercury and composed of carborundum or boron carbide. This type of starting electrode is well known in the art and is more specifically described in Patent No. 2,069,283, issued February 2, 1937, to Joseph Slepian.

The two devices |8 and H! are disclosed in order that both directions of the alternating current may be controlled in the application to the welding circuit, since each device acts as a rectifier as well as being a controllable conductor.

When a certain amount of current is caused to flow through the starting electrode 23 into the mercury pool 2|, a cathode spot is formed which furnishes a source of electrons which in turn causes ionization of the mercury vapor within the container 2| and, under the influence of positive anode potential, the tube becomes 'conducting. Thus, it is only necessary to pass suflicient starting current through the starting or ignition electrode 23 to form the cathode spot at a predetermined time in the proper half cycle in the alternating current wave to render the vapor electric devices conducting for the remainder of that particular half cycle. In order to conduct succeeding half cycles of alternating current, the vapor" electric devices I8 and I! are connected inversely. That is, the anode 20 of device I8 is connected to the cathode 2| of device l9, and the anode 20 of device |9 is connected to the cathode 2| of device l8. It will, therefore, be evident that if the vapor electric devices It! and I9 are energized in turn during successive half cycles, current from the source of alternating current will flow to the transformer ID as long as this condition is maintained.

A preferred embodiment of the automatic means for completing the application of the electrodes to the part i5 is disclosed on the drawing. It is generally advisable to attach such means only to one of the electrodes because the workmen can apply one of the electrodes to the parts and then start the apparatus to apply the other electrode thereto. Accordingly, I have disclosed only the automatic application of one of the electrodes to the work, although it is apparent that such application might be made to both electrodes if such were desired. The electrode I4 preferably has a shaft I extending into a casing I3I, and this shaft has a plunger I32 actuated by the pressure within the casing. A spring I33 preferably surrounds the shaft to withdraw the electrode from its operative position when the pressure is released. A vent I34 provides release of atmosphere on the forward side of the plunger.

A reservoir I provides the pressure medium which might be compressed air or oil or any similar desired medium for conveying the pressure. This air reservoir is connected to a valve casing I36 having a valve I31 under pressure of a spring I38, normally maintaining the valve. closed. The valve may be opened by a relay I39 actuating a shaft I connected to the valve I31. When the shaft is actuated, a valve I4I closes the opening I42 and the medium under pressure passes from the reservoir or pump I35 through a chamber I143 and conduit I44 to the portion I of the easing I35, and presses the welding electrode I4 in contact with the object or objects I5 to be welded.

A conduit I46 is also preferably connected to the conduit M4 to operate a switch H41 for actuating the control system of the welding current at the time that the electrode is applied to the work. Upon completion of the desired number of half cycles or" welding current, the relay M8 will be operated by the control system to break the current at switch 149 and release the pressure on the electrode i i and the switch 541 to interrupt control circuit. If it is desired to make any slight time delay or lag in releasing the electrode or the switch 341, damping means i156 may be applied to the relay M8. The switch I55 actuates the application of the current from it and ii to the relay H39, actuating the pressure means.

While various control systems might be devised for the automatic application of the current to the electrode and the application of the electrode to the work, I prefer to modify the system disclosed in the copending application of John W. Dawson, Serial No. 142,564, for Welding timing circuits, filed May 14, 1937.

The control system. involves the utilization of control tubes for supplying ignition current to control the discharge in the tubes i8 and i9 and also electronic devices for accurately operating and stopping the operation of these tubes at predetermined points on the half cycles of alternating current. In the preferred embodiment illustrated, I utilize tubes 24 and 25 for controlling the discharge in the devices I8 and i 9 through the igniter or starter 23 and then I utilize a starting tube 26, a cut-off tube 21 for the discharge and in addition for starting the discharge at a predetermined point on the first half cycle of the power period a further tube 28. The application of. this control system is preferably instituted by an externally operated switch 29 which may be operated manually or by a cam on the welding machine. In other words, when the operator desires to perform the welding operation, he depresses the switch 29, energizing the relay 3t from the conductors 34, 32 connected to the source of alternating current. The relay 30, in turn, operates various individual switches hereinafter referred to in the description of the control circuit.

The cathodes of the tubes 24 and 25 are energized from the alternating circuit by transformers 33 and 34, respectively. The midpoint of the secondary of the transformer 33, namely 35, has a connection 36 extending to the ignitor or starter 23 of tube I 8. Likewise, the midpoint 38 of the secondary of transformer 34 is connected through connection 39 to the starting electrode 23 of the tube I9. The anode II of tube 24 is connected through resistance 31 and switch point 42 of the starting relay 3!] to the connection 43 to the anode 20 of tube I8. The anode 44 of tube 25 is likewise connected through resistance 40 and switch 45 of the relay 30 to the connection 46 to the anode 20 of tube I9. The grids 41 and 48 of tubes 24 and 25 are connected through suitable resistances 49 and 50 to opposite ends of the secondary 5| oi transformer 52 connected to the source of alternating current. The grids and cathodes of tubes 24 and 25 may be energized from secondary windings on the same transformer instead of the individual transformers disclosed. Between the conductors 43 and 46 extending to the cathodes and anodes of the tubes I8 and I9 previously described is a resistance 53. The variable tap 54 on this resistor is to compensate for any slight difference between the tubes I8 and I9 in operation.

The further function of this resistance 53, together with the transformer winding 5i connecting the grids and cathodes of the tubes 24 and 25 is to nullify the alternating-current potential which would otherwise exist on the grids 51 and 48 of tubes 24 and 25, because of their circuit locations.

Tube 26 is utilized as a starting device. Its cathode $9 is energized through the secondary ii of transformer 62 and the midpoint $3 of this secondary is connected through the midpoint 5d of resistance 85 and connections 65 to the midpoint 81 of the transformer secondary con nected to the grids ll and d8 of the tubes and 25. The anode $8 of tube 26 is connected to the positive terminal 69 of a source of direct current potential disclosed as the rectifier grid 1d which is connected to a transformer ii, energized from the source of alternating current. The negative terminal 12 is connected through conductor 73 to the resistance 55, cathode transformer secondary 6i and cathode 69. The grid 14 of tube 26 is connected through a connection 15 to the negative terminal 16 of a similar rectifier bridge '11 also energized by the alternating-current source. These rectifier bridges are preferably of the well known copper oxide dry plate type. The negative potential'from the rectifier bridge 11 on the grid 14 constitutes a discharge preventing bias normally applied to the control electrode of the starting tube 26.

The operation of the starting tube 26 is controlled by means of the timing tube 28 previously referred to which controls the point of initiation of tube 26 with respect to the voltage wave. This timing tube 28 is preferably of the hot cathode gaseous discharge type and is provided with a phase shifting control circuit 89 for the grid 2i of the tube. This phase shifting control circuit comprises an adjustable resistor 32 and an adjustable capacitor 83. The phase shifting circuitv 8!] is connected by means of a transformer $5 to the same source of alternating current as is applied to the anode 85 and cathode 86 of the timing tube 28. Alternating current for the timing tube 28 is provided from windings on the secondary of transformer 84. The output of timing tube 28 is applied to a circuit comprising the resistor 91 and a winding d8 of a transformer 89. The

secondary winding 90 of the transformer 80 is indirectly connected to the grid 14 of the starting tube 26 when the switch I20 of relay 30 is closed through the connection 15 which, as previously described, normally applies a negative discharge preventing potential to this grid 14.

The phase shifting circuit 80 is adjusted by means of the variable resistors82, and variable capacitor 83 to render the start tube 26 conducting at the desired point in the cycle of operation of the alternating current source. The phase shifting circuit 80 will determine the exact point on the voltage wave that the tube 28 will be rendered conducting. The discharge in tube 28 permits current to flow through the primary winding 88 of transformer 89 and due to the steep wave front of the current applied, a sharp voltage surge will appear in the secondary winding 90 which will be applied, in turn, to the grid 14 of the starting tube 25. The peak value of the surge is suflicient to overcome the negative potential of the source 11 and to positively bias the grid 14, thereby rendering the start tube 26 conducting. As soon as the start tube 25 becomes conducting, a positive potential is applied to the control tubes 24 and 25 and they will then function to establish the conductivity of tubes I8 and I9. 1

It will be noted that the cut-oi? space discharge device 21 has its anode I connected through switch IM to the same positive terminal of the recti fier bridge 10 as the anode 68 of the starting tube 26. The cathode i02 of the cut-off tube connected through the midpoint i'03 of the transformer secondary M4 by means of a connection E05 to the midpoint 54 of the resistance 53 across the anodes and cathodes of the tubes 58 and iii. The grid 506 of cut-oif tube 21 is connected through adjustable resistance i 01 to the cathode circuit 60 of the starting tube 20. An adjustable timing condenser E08 is connected to the cathode circuit 63, fit of starting tube 26 and to conductor extending from the negative terminal of the direct-current rectifier bridge 10 to the resistance 65. The resistance or voltage divider I09 extends from the connection 99 between the anodes of tubes 26 and 21 to the point H0 on the conductor 13 connected to the grid i06 of tube 21. A tap I I I is taken from a point on the potentiometer and by means of connection II2 is applied to the cathode circuit I02 of the cut-off tube 21. It will be noted that the point IIO with respect to junction III corresponds to the negative grid potential of the cut-off tube 21. The point II I corresponds to the cathode potential of the tube 21.

The conduction of the tube 26 will apply potential across the resistor 65 and this potential acts to charge the condenser I08 through the variable resistance I01. After a time variable by adjustment of resistor I01, condenser I08 is sufficiently charged to raise the grid I05 of tube 21 to its breakdown point with respect to its cathode I02. With the breakdown of this tube, positive potential is fed through the tube and its cathode transformer to wire I05, which action again throws the bias on control tubes 2 and 25 to a negative value stopping the further ignition of the tubes i8 and I9 and hence further welding currents after the termination of the particular half cycle. Leads 66 and I05 are the timing circuit output leads.

Whe neither tube 26 nor 21 is ignited the lead 66 is negative to lead I05. When the start ing tube 25 discharges, the lead 66 becomes positive and the lead I05 becomes negative. When the stop tube ignites, the lead 66 again becomes negative in respect to the lead I05. During the period while lead 66 is positive in respect to lead I05, welding current can flow.

The weld has, accordingly, been completed by the automatic operation of tubes accurately timing the predetermined number of half cycles of alternating current. No manual operation by the operator in connection with the control circuit is necessary after the work I5 is in position, except for the depression'oi the manual switch 29. The sequence of the switches operated thereby is first switch IM to complete the output circuit of rectifiers 10 and 11, then switches 45 and 42 together and then I20. After the weld has been completed, the pressure is released from switch 29 and the various switches operated by relay 30 will be released in reversed order, namely I20, 42 and and then IOI, but the connection at switch II5 will be made to discharge the timing condenser I08 and have it ready for the next operation.

It will be noted that both the negative component of the timing voltage applied to tube 21, i. e., between H0 and III, and the positive component of timing voltage, 1. e., the voltage across I08, is derived from the same source 10, and, accordingly, variations in this source due to changing of temperature or other causes will equally efiect the positive and negative components of grid voltage as applied to tube 21 and will not change therefore the accuracy of timing following the discharge of tube 26.

Various condensers and resistances are, of course, illustrated at desired places in the apparatus, some of which, as at 56 and H1, act-as filters.

The pressure means described in the first part of the description is actuated by the relay F39 Whose actuating current is controlled by the rela M8. This relay 548 is inserted between the point 1 on the potentiometer i539 and its connection to the resistance iii. When the stop tube .2! actuated by the discharge of the condenser M2, the change in current from point iii through conductors 52 and 553 will actuate the reiay H8 to open the switch M9 and withdraw the actua- 'tion of the pressure means by closing the valve 31. The release of the pressure in chamber I36, conduit I44 and chamber I45 through the vent I54 in casing I35 will permit the spring I33 to withdraw the electrode I4 from the work I5.

My invention accordingly permits the accurate application of the exact number of half cycles necessary for a welding job to be applied thereto. and the automatic withdrawal of an electrode from such work upon the completion of the application of these half cycles to the work. The saving in both electricity and time of the workmen in. large and fast moving assembly lines through the utilization of my invention should be apparent. It is also obvious that the workmen do not need to be highly skilled in the work as formerly, because the apparatus can be set by one highly skilled workman and the actual work performed by another who has merely to apply one of the electrodes to the work.

It is apparent that many modifications may be made in the specific form of the pressure and control means illustrated in my preferred embodiment. Accordingly, I desire only such limitations to be placed on the following claim as are necessitated by the prior art.

I claim as my invention:

In combination, a pair of welding electrodes for application to parts to be welded, an'alternating current welding circuit connected to said welding electrodes, a discharge device having a portion of said alternating current welding circuit therethrough, an electrode in said device controlling the passage of the alternating current through said device and circuit, circuit means applied to said electrode stopping the discharge therethrough after a predetermined number of half cycles, pressure means completing the application of the electrodes to the parts to be welded, said circuit means automatically releasing said pressure means upon the completion of the predetermined number of half cycles.

RALPH N. STODDARD. 

